Formula used
This calculator uses a planning model that converts a detector’s rated zone into a usable coverage area, then applies derating factors for real-world conditions.
BaseArea = BeamLength × CorridorWidth (open-path)
EffectiveArea = BaseArea × Fheight × Fvent × Fobstacles × Fgas × Foverlap × Fpattern
Detectors = ceil( (ZoneArea / EffectiveArea) × (1 + Safety%) )
For rectangles, a grid check is also performed using the suggested spacing, and the final recommendation uses the larger of the two counts.
How to use this calculator
- Choose units and enter a zone name for your report.
- Select the zone shape and provide dimensions or a total area.
- Pick a detector technique and enter the rated radius or beam details.
- Set ceiling height, ventilation, and obstruction levels for derating.
- Match mounting level to gas behavior, then set overlap and safety.
- Click Calculate coverage and review spacing and grid outputs.
- Use the download buttons to export a CSV or PDF report.
Example data table
| Scenario | Zone | Technique | Inputs | Typical output |
|---|---|---|---|---|
| Mechanical room | 24 × 18 m, 3.5 m ceiling | Point | r=6 m, medium ventilation, moderate obstacles, 15% overlap, 10% safety | ≈ 3–4 detectors, spacing ≈ 9–10 m |
| Parking bay strip | 60 × 12 m, 4.0 m ceiling | Open-path | Beam 20 m, corridor 4 m, high ventilation, moderate obstacles | ≈ 9–12 beams depending on layout |
| Generator enclosure | 12 × 10 m, 3.0 m ceiling | Point | Heavier gas, low mounting, low ventilation, 20% overlap | ≈ 2–3 detectors, tighter spacing for pits |
| Compressor skid | 20 × 15 m, 6.0 m structure | Ultrasonic | r=8 m, high ventilation, heavy obstacles, 15% overlap | ≈ 5–7 detectors near leak sources |
Examples are illustrative; always validate with project requirements, manufacturer guidance, and regulations.
Define the monitored zone and leak sources
Start by setting a clear zone boundary: one room, one bay, or one corridor segment. The calculator converts length and width into area, then uses ceiling height for coverage derating. For mixed elevations, split the space into smaller zones. List likely leak points such as valves, flanges, regulators, and hose connections to avoid assuming uniform risk.
Select a detection technique with realistic geometry
Point sensors provide localized coverage around equipment clusters, while open-path beams suit long runs where gas can drift along a line of travel. Ultrasonic detection targets pressurized leak noise, especially in high-airflow structures. Enter a rated radius or beam length from the datasheet and keep it conservative when access constraints limit placement options.
Account for ventilation and obstructions
Higher ventilation disperses gas and can delay accumulation at a sensor, so this model applies a ventilation factor (low 1.00, medium 0.90, high 0.80). Obstructions create shadow zones and stratification, so the obstruction factor reduces usable coverage (none 1.00, moderate 0.85, heavy 0.70). Use “heavy” when partitions, racks, or dense machinery dominate sight lines.
Control overlap, spacing, and safety margin
Overlap reduces the effective area per detector to avoid uncovered gaps; a 15% overlap keeps spacing tighter without overbuilding. The suggested spacing is a planning guide derived from effective coverage, not a code requirement. Add a safety factor when future equipment changes are likely, when the gas release rate is uncertain, or when detectors must be offset from ideal locations.
Document assumptions and verify deliverables
Use the notes field to record target gases, mounting constraints, and any excluded volumes such as sealed shafts. Then compare outputs with project specifications, manufacturer guidance, and local regulations before issuing IFC drawings.
Technique: Point • Rated radius: 6 m • Vent: Medium • Obstacles: Moderate
Overlap: 15% • Safety: 10% → Typical result: 3–4 detectors
FAQs
What does “effective area per detector” mean?
It is the rated coverage area after applying derating for ceiling height, ventilation, obstacles, mounting match, overlap, and grid efficiency. It represents the usable planning coverage per detector in your selected units.
How should I choose the rated coverage radius?
Use the manufacturer’s published planning radius for the target gas and environment. If conditions are uncertain, choose the lower value and increase overlap or safety factor to maintain conservative coverage.
When is an open-path beam a better choice?
Open-path is effective for long corridors, loading bays, or perimeter coverage where a gas plume may pass through a line. It is less suited to small rooms with complex obstructions and tight corners.
Why does higher ventilation increase detector count?
Airflow can dilute and transport gas away from a detector, reducing the chance of timely detection at any single point. The model decreases usable coverage as ventilation increases, which raises the recommended detector quantity.
Does this replace code-required spacing and design rules?
No. This tool supports early planning and scenario comparison. Final spacing, mounting heights, and device selection must follow the detector manufacturer, project specifications, and applicable standards and authority requirements.
How do I handle irregular or multi-bay spaces?
Use “Custom area” for quick estimates, or split the space into separate zones that better match real boundaries and airflow paths. Calculate each zone and sum detectors where separation is practical.
How should pits, trenches, or ducts be treated?
Model them as separate low-level zones for heavier-than-air gases, or add dedicated point sensors at low points where gas can collect. Increase overlap and reduce assumed radius when access or airflow is limited.